METHOD FOR THE MANUFACTURE OF A MAT-LIKE PRODUCT

Abstract: In a method for making a fibrous product from separate particles, an air flow (A) is used for forming a mat on an advancing forming platform (1). The particles are bonded to form the mat by means of thermally activatable binder material brought to the mat forming site such that it upon being activated through the action of heat bonds the particles to each other in the mat. Said binder material is brought to an activated state already in air flow (A) carrying the particles onto forming platform (1) by setting temperature of the air flow sufficiently high. The material forming the base of the mat in the particles is constituted of a material activatable at a higher temperature than the thermally activatable binder material.

Description: Method for the manufacture of a mat-like product The present invention relates to a method as set forth in the preamble of the appended claim 1 for the manufacture of a mat-like product. International publication No. WO 82/03359 discloses a method for making a moldable mat from wood fibers such that the wood fibers are intertwined with thermally bondable binder fibers which bond the fibers together upon melting and setting. The mat is formed by using a so-called dry process on a moving belt by means of an air flow, which transports the fibers onto the belt and travels through the mat. This is followed by a mat bonding process by carrying the thus formed mat through an oven, having a sufficiently high temperature for softening the binder fibers, which are of thermoplastic plastics material, and bringing them in an adhesive state for bonding the wood fibers to each other. The use of wood fibers and other cellulosic fibers of vegetable origin for manufacturing products made of fibers is attractive in the sense that the question is about reclaimable natural raw materials, which are abundantly available, pleasant to handle as a material, and do not create health hazards. A fibrous mat manufactured from these fibers is also an effective heat insulation. However, this is the very feature that causes a problem in manu¬ facturing the product, if the above process is to be employed. When treating the product in an oven, it is namely necessary to give the oven a considerable length for heat to penetrate also in the interior of a mat-shaped product for bonding the fibers. If the purpose is to manufacture products of considerable thickness, it would be necessary to make the ovens unreasonably long for bonding the mat properly also in its middle sections upon leaving the oven. Another alternative would be a drastic increase of temperature which would, however, lead to damages in the surface structure of a product, since the thermoplastic fibers included therein would then melt or fuse completely away as globular drops not capable of bonding the fibers together and the mat would break up. It is obvious that the above processes are not feasible in terms of energy consumption, either. For eliminating this drawback, Finnish Patent Application No. 922421 discloses a method as well as an apparatus, by means of which it is possible to manufacture even very thick fibrous mats of wood fibers having an excellent heat insulation capability. Here thermoplastic binder fibers acting as heat-activatable binder material and intertwined with vegetable-based cellulosic fibers are activated, i.e. softened already in an air flow carrying the fibers to a forming platform by setting the temperature of the air flow sufficiently high. The heat insulation properties of the fibers will thereby not be detrimental. Thermoplastic binder fibers bond wood fibers to each other already at the manufacturing stage of a mat. In practice, this facili- tates the manufacture of even a very thick mat, since fresh fibers bonding into a mat can be stacked basically in quantities as large as may be desired on top of a mat previously formed at the manufacturing site of a mat. The above-mentioned method is restricted to the use of cellulosic fibers. Now it has been discovered that the method is also suitable for manufacturing such products where instead of the cellulosic fibers which are not activatable by heat, the base material forming the mat can be constituted of particles activatable at a higher tempera¬ ture than the binder material, such as of mineral fibers ("rock fibers" and glass fibers) or other thermoplastic fibers. The invention will now be described in more detail with reference made to the accompanying drawings, in which fig. 1 is a cut-away side view of a mat forming assembly included in an apparatus used in the method of the invention, fig. 2 is a cut-away plan view of the assembly shown in fig. 1, fig. 3 is a larger-scale view of a detail included in the assembly shown in fig. 1. fig. 4 illustrates schematically the operating prin¬ ciple for an entire apparatus. Fig. 1 illustrates a mat forming assembly, including a feeding mechanism 11 for separate particles. The feeding mechanism may comprise either a per se known vertical device lla for bringing the particles by means of an air flow, or a horizontal conveyor lib, whose inlet end can be provided with per se known pretreating means. The bottom end of feeding mechanism 11 is provided with a feeding roll 2 having pins on its surface in a dense pattern. Facing towards the surface of feeding roll 2 is a horizontal narrow slit orifice at the end of a first air conduit 3. Below the slit orifice is located an inlet for a second air conduit 4, with a constriction point formed between its bottom wall and the surface of feeding roll 2. Downstream of this constriction point there is an obliquely declining, expanding air chamber 6, having its lower end closed with an air permeable forming platform 1. On the opposite side of forming platform 1 lies a collecting chamber 10. The forming platform 1 is formed of an endless belt, extended around cylinders and adapted to travel across chamber 6. Downstream of chamber 6 said forming platform travels across a second air chamber 8, providing a bottom surface therefor. The inlet end of first air conduit 3 is provided with mutually parallel fans 12 for producing a uniform air flow across the entire width of duct 6. These fans 12 are shown by dash lines in fig. 2. A duct serving as the inlet end of second air conduit 4 is also provided with a fan 13, which is adapted to blow air heated by a heater 7 into said second air conduit 4. Heater 7 can be for example a conventional gas burner. The mat-forming process in the apparatus is such that separate particles forming base structure of the mat, which have been manufactured earlier, are delivered by means of the feeding mechanism towards feeding roll 2. Fig. 4 shows the subsequent mat-forming process in more detail. The rotating feeding roll 2 includes pins 2a, indicated in the figure as the outermost layer of the feeding roll, for picking up and carrying the particles further. In the rotating direction of the feeding roll, the fibers arrive next in the range of action of a horizon- tal slit orifice 3a, located at the end of first air conduit 3 and extending across the width of said roll. A high¬ speed air flow Al discharging from the slit orifice dis¬ engages the particles from feeding roll 2 while rushing along the roll surface and carries them across the inlet 4a of second air conduit 4 into a constriction point 2b between the bottom wall of said inlet 4a and the surface of feeding roll 2. After the constriction point, the particles are completely disengaged from feeding roll 2 and proceed into an air chamber 6, having a cross-section which expands in their advancing direction and having a width which is constant and corresponds to the width of a mat to be manufactured. The expansion or flare of the chamber is achieved in a manner such that the front and rear walls, extending in the axial direction of feeding roll 2, i.e. in the lateral direction of a mat being manufactured, diverge from each other. Said second air conduit 4 is used for delivering air as an air flow A2 into said inlet 4a. The temperature of this second air flow A2 is higher than that of said first air flow Al supplied through said first air conduit 3. As a result of the ejector effect produced by constriction point 2b, this air flow A2 merges into air flow Al and blends therewith for an air flow A carrying particles to the outlet end of air chamber 6. The supply rate of this higher- temperature air flow A2 is arranged to be such that the temperature of air flow A carrying the particles in air chamber 6 is sufficient to cause the activation of a thermally activatable binder material blended with the particles to a degree that makes it capable of bonding the particles into a mat. However, this temperature is lower than the activation temperature of the separate particles forming the base of the mat, such that essential changes do not occur in this material. This thermally activatable binder material is well exposed to the action of aiz, since they travel in the air flow in bare condition either as separate binder particles, such as binder fibers, or incorporated in the particles on the surface of the material forming the base of the mat. The outlet or trailing end of air chamber 6 is closed by a forming platform 1, which travels across the chamber and can be a woven wire fabric or a like air-permeable flat piece of material. The particles hitting the bottom at the inlet of a conveyor, i.e. downstream of the air chamber front wall, immediately build up a bonded mat and an identically bonded mat of a continuously increasing thickness begins to gather on top of that. Since the resulting mat is porous in nature, said air flow A is able to progress through the mat and said forming platform 1 therebelow into a collecting chamber 10 on the opposite side. Fig. 1 illustrates the subsequent processing of a mat. Downstream of chamber 6 in the traveling direction of forming platform 1 is mounted a packing cylinder 14, whose distance from forming platform 1 is adjustable. The packing cylinder prevents the passage of air in the traveling direction of forming platform 1 out of the air chamber from above the mat. Downstream of the packing cylinder, said forming platform 1 carries the mat into a second air chamber 8 located above forming platform 1. The top end of air chamber 8 is provided with an air conduit 9. The second air chamber 8 has a flaring or expanding configuration towards forming platform 1 in the flowing direction of an air current supplied from air conduit 9, i.e. the chamber walls located on the inlet and outlet side of the forming platform are diverging from each other. For example, the pressure of an air flow B supplied into the chamber can be applied for further compressing the mat to a desired degree for providing a desired value for its density. Thus, the air flow is delivered through the porous mat and the forming platform 1 supporting it from below and into a second collecting chamber 15 located on the opposite side. Thus, said air flow B supplied into second air chamber 8 has such a temperature that the binder fibers still remain in a softened state where the fibers allow the deformation of the mat for shaping or molding the mat to a desired density such that the deformation is permanent. Downstream of second chamber 8, the mat is transferred from forming platform 1 onto a conveyor 16 for carrying the bonded mat- shaped product forward for further processing. If a product of a particularly low density is desired, the further processing effected by means of second air chamber 8 can be omitted. The product density can also be controlled already during a mat-forming operation by means of the flow rate of air current A advancing in air cham¬ ber 6, said flow rate dictating the force by which the fibers strike into a mat configuration. Fig. 4 illustrates schematically one possible arrangement for air flows in the invention. The air currents are circulated such that the mat-forming air flow or current A arriving in collecting chamber 10 is delivered by way of fan 12 into first air conduit 3. During this period the air flow has time to cool to such a degree that the first air flow Al discharging from air conduit 3 through slit orifice 3a is below the temperature capable of bringing the binder material to an activated state. Thus, this air flow Al only serves for detaching the particles from feeding roll 2. However, it can be used for providing a preheating, whereby the air flow A2 discharging from air conduit 4 need not be given a particularly high temperature. Said air flow A2 is delivered into second air conduit 4 from heater 7 by means of fan 13. The air conduit 4 branches for an air conduit 9 connected to second air chamber 8, whereby some of the heated air flow Al blown by the fan is extracted as an air flow B performing the further processing of a mat. This also secures that in the further processing said air flow B has a sufficiently high temperature and, since it originates from air conduit 4, which only contains the flow of heated air, its temperature is in fact higher than that of air chamber 6. However, this air does not harm the material, as it is less exposed to it, surrounded by the mat base material contained in the articles and, on the other hand, the flow rate of air per unit area remains quite low due to the extent of chamber 8. The air flow B received in second collecting chamber 15 on the other side of forming platform 1 is circulated back to heater 7 by way of an air conduit 18. The chamber 8 also receives air carried along with a mat from chamber 6. This air advances through collecting chamber 15 merging with the return air flowing to heater 7. In order to maintain the air balance, some of the air progressing in first air conduit 3 is delivered out along a duct 17. This is compen¬ sated for by delivering to heater 7 not only circulated air but also compensation air from outside. Air can also be circulated from duct 17 to heater 7, but this degree of circulation is determined by impurities accumulated in the air during the mat manufacturing process. Fig. 4 further illustrates normal measuring and regulation equipment for setting the temperatures of air flows as desired. All possible product forms are conceivable for the product manufactured in accordance with the invention, starting from a flexible mat to a stiff plate, in a wide range of grammages. All particles activatable at a certain temperature to a state where they become bonded to each other can be applied in the method as the particles forming the base structure of the mat. Such particles can be fibers which have been originally manufactured of a molten material, such as mineral melt ("rock fibers" i.e. rock wool fibers, and glass fibers) , or thermoplastic plastics material. The density of the mat can be influenced by selection of the fiber grade and ratios. It is, nevertheless, possible to use also particles of other kind which can be made to form a mat by means of an air flow. One example of the thermally activatable binder material that can be used is thermoplastic material, such as ther¬ moplastic polymer, of which can be mentioned polypropylene and polyester. The thermoplastic material is activated to a bonding state when it softens under the influence of heat. It is also possible to employ bicomponent material containing polymer softening at a lower temperature on the surface of the particles. Such particles, for instance bicomponent fibers, can be used either as the binder material for binding other particles, which form the base, or as the particles themselves forming the base, whereby their material activatable at the higher temperature serves as the mat base forming material. The temperature of air current A flowing in air chamber 6 can be set according to the activating point of a binder material and this point, at which the binder material softens to an adhesive or tacky state, is within the range of 100...200°C on the most commonly used thermoplastic polymer materials. The activating temperature of the material forming the base is higher than this. It is thus possible to employ a higher-melting thermoplastic material as the base material and a lower-melting thermoplastic material as the binder material. The mat structure can also be controlled by selecting the proportions between the thermoplastic binder material and base material. The basic raw material for the structure of the product consists of the base material, which preferably makes up most of the total mass of a mat. The resulting mats can have weights per unit area within the range of 40 g/m 2 - 3000 g/m 2 , and their densities can range from 18 kg/m 3 to 400 g/m 3 . The products obtained can be used, depending on the kinds of particles and the mat thickness and stiffness, for various applications, such as heat insulation, filters, lining of various interiors such as buildings and vehicles, etc. The product can also be used for various applications in the form of a half-fabricate that can be pressure-molded again by heat. The obtained products can also be after- treated for improving some properties.

Claims: Claims 1. A method for the manufacture of a mat-like product, wherein an air flow (A) is used for forming a mat from separate particles on an advancing forming platform (1) and the particles are bonded to form the mat by means of thermally activatable binder material brought to the mat forming site such that it upon being activated through the action of heat bonds the particles to each other in the mat, said material being brought to an activated state already in said air flow (A) carrying the particles onto forming platform (1) by setting temperature of the air flow sufficiently high, characterized in that the material forming the base of the mat in the particles is constituted of a material activatable at a higher tempera¬ ture than the thermally activatable binder material. 2. A method as set forth in any of claims 1-6, charac¬ terized in that the binder material is on the surface of the particles brought to the mat forming site. 3. A method as set forth in claim 2, characterized in that the particles are bicomponent fibers, where the binder material is on the surface of the fibers. 4. A method as claimed in claim 1, characterized in that the binder material is in the form of particles that are separate from the mat forming particles. 5. A method as claimed in claim 4, characterized in that the separate particles are base fibers forming the base material of the mat, and the particles of the binder material are binder fibers. 6. A method as set forth in any of claims 1-5, charac¬ terized in that the separate particles introduced towards the mat forming site first by means of a first air flow (Al) which is thereafter supplemented by a higher- temperature second air flow (A2) , as a result of which the temperature of a combined air flow (A) produced by said air flows (Al, A2) increases such that the binder material is brought to an activated state. 7. A method as set forth in any of claims 1-6, charac¬ terized in that, after being formed by means of the air flow (A) on forming platform (1) , said mat is processed further by delivering a flow (B) of gaseous medium through the mat while the mat is supported from the side opposite to the flowing direction of the air flow. 8. A method as set forth in claim 7, characterized in that the further processing comprises increasing the mat density by means of a pressure produced by an air flow (B) against the mat. 9. A method as set forth in any of claims 6-8, charac¬ terized in that the first air flow (Al) and said higher- temperature second air flow (A2) are supplied along their own air conduits (3, 4) and the air flows are circulated such that, after flowing through forming platform (1) , some of the air flow (A) having accomplished the formation of the mat is delivered into the air conduit (3) of the first air flow (Al) for preheating the air flow. 10. A method as set fort in any of claims 7-9, charac¬ terized in that some of the higher-temperature air flow (A2) progressing in the air conduit is delivered to the aftertreatment of the mat, whereby that flow makes up at least some of the air flow (B) delivered through the mat.

Inventors: NIEMINEN JORMA, NIEMINEN, JORMA
Applicants: NIEMINEN JORMA, SCANWOVEN AB OY, NIEMINEN, JORMA, OY SCANWOVEN AB
Application year: 1994
Main classification: B27N3
IPC codes: B27N3